1. Field of the Invention
The present invention relates to an optical recording and playback device which records and reads code information, and audio and video information using an optical read/writable medium by means of a semiconductor laser or other light source.
2. Description of the Prior Art
A prior art optical recording and playback device is shown in FIG. 1, which uses an optical disk 1 on which a data recording/playback track 2 is formed. The light beam 4 emitted by the laser diode 17 is converted to a parallel beam by the collimator lens 18, passed through the half mirror 19, and focused to a spot 3 by the objective lens 5 on the optical disk 1. The light reflected from the optical disk 1 passes the objective lens 5 and is partially reflected by the half mirror 19 to the half mirror 20, which splits the beam in two. The reflected light from the half mirror 20 passes the coupling lens 21 and is converted to an electrical data read signal by the photodetector 22 which is applied to the playback signal detector 7. The light which passes through the half mirror 20 is again split by another half mirror 23.
The light reflected by the half mirror 23 passes the coupling lens 24 and is partially blocked by knife edge 25, the unblocked part is incident upon a 1/2 divided photodetector 26, and an electrical focus error signal is detected by a differential amplifier 8. Phase compensation and other processing is applied to the focus error signal by the focus servo circuit 9, and the light beam 4 is focused on the recording medium surface of the optical disk 1 by moving the objective lens 5 in a roughly vertical perpendicular direction to the optical disk 1 surface by means of the focus actuator 10 according to the output of the focus servo circuit 9.
The light passing through the half mirror 23 passes the coupling lens 27 and is incident upon the 1/2 divided photodetector 28, and is converted to an electrical tracking error signal by the differential amplifier 11. Phase compensation and other processing is applied to the tracking error signal by the tracking servo circuit 12, and the spot 3 is tracked along the data recording/playback track 2 by moving the objective lens 5 laterally in an approximately perpendicular direction to the track 2, i.e., perpendicular direction to the sheet when viewed in FIG. 1, by means of a tracking actuator 13 based on the output of the tracking servo circuit 12.
The output of the tracking servo circuit 12 is also input to the traverse servo circuit 14, which applies phase compensation and other processing before outputting the signal. The traverse servo circuit 14 is used to drive the linear motor 15 to move the optical head 6 fixed to the transport block 16, the focus actuator 10, and the tracking actuator 13 in a roughly laterally perpendicular direction to the signal recording/playback track 2, as effected when jumping a number of tracks.
In the prior art optical recording and playback device, a light beam generated by a semiconductor laser or similar light source is focused on a disk-shaped recording medium rotating at a predetermined velocity to record and playback a signal thereon. This recording medium typically has a spiral recording track or concentric recording tracks approximately 1.2 .mu.m wide at an approximately 1.6 .mu.m pitch. To record a signal on this track or read a recorded signal back from this track, a focusing servo focuses the light beam to a microscopic light spot with a maximum 1 .mu.m diameter on the disk surface, a tracking servo causes the light spot to track the signal track, and a traverse servo moves the optical head in a direction approximately perpendicular to the signal track.
However, to stabilize servo operation for the prior art optical recording and playback device as thus described, a technician must measure the frequency characteristics of the focusing, tracking, and traverse servo loops using a spectrum analyzer or other frequency characteristics analyzer, and adjust the potentiometers provided to change the gain of the servo signal processing circuits to the specified servo gain level. In addition to this servo gain adjustment procedure being time consuming, when the characteristics of the servo error signal detection sensitivity of the optical head, the actuator, and the linear motor change due to temperature changes, the servo loop gain also changes, resulting in an unstable servo operation.